Devices for regulating the flow of a liquid are known. German Offenlegungschrift No. 26 44 140, for example, shows the cross-section of a valve opening which is regulated with a needle-valve axially moveable by a thread. The corresponding thread bolt extends through the housing to the outside and is manually actuated.
Disadvantages have been experienced in the use of devices of the prior art. The use of seals allows germs to migrate along the thread from the outside to the inside which, during the use for intravenous infusion, may lead to an infection of the patient. Moreover, air may enter along the thread of the needle valve which may result in great danger to the patient if an air bubble enters a vein.